Confer Plastics, Inc., the assignee, has been manufacturing plastic products for more than 30 years. It has obtained a few patents directed to how to interconnect plastic materials together. One of those patents is U.S. Pat. No. 6,190,600. In view of Confer's experience in the plastic industry and obtaining patents, Confer is familiar with various methods to interconnect plastic pieces together.
The conventional method to interconnect plastic pieces together is to have a tongue and groove system with an additional interlocking device. That additional interlocking device includes screws. Screws and conventional metallic interconnecting components however deteriorate the integrity of the plastic material. As such screws and other metallic interconnecting components are to be avoided as the additional interlocking device.
To address that problem, the additional interlocking device has included an additional male component interlocking with an additional female component wherein the male component is incorporated in the original tongue system and the additional female component is incorporated in the original groove system.
An example of the tongue and groove system with additional male and female components is found in Confer Plastics' Leisure Accents step ladder. The Leisure Accents step ladder, as illustrated in FIGS. 1 to 4, has at least two identical side walls 10 (two are illustrated by broken lines in FIG. 1 and one is shown in FIGS. 2, 3, and 4), a interconnect base board 20a, a terminal base board 20b (see FIGS. 1, 2, and 3), an interlocking step 40a and a terminal step 40b (shown at FIGS. 3 and 4). Each side step side wall 10 has a first riser section 12a for the interconnect base board 20a, a second riser section 12b for the terminal base board 20b, a first tread section 14a for the interlocking step 40a, and a second tread section 14b for the terminal step 40b. Each riser section 12 has a tongue section 16a and each tread section 14 also has a tongue section 16b. The tongue section 16a, 16b extends the length or at least the majority of the length of the respective section. At a predetermined position (can be a different position for each riser section 12 and tread section 14) on the tongue section 16a has at least one male component 18a, and the tongue section 16b has at least one male component 18b. The male component 18a,b is hour glassed shape or variations thereof as illustrated in FIGS. 2 and 3.
Each base board 20 has an exposed surface 22, an opposite surface 24, a proximal end 26 (closest to the ground) and a distal end 28. As illustrated in FIG. 3, the base board's 20 opposite surface 24 has a groove section 30 and a female component 32 that respectively receive the riser's tongue section 16a and male component 18a. In particular the female component 32 has a rib area 34 that conforms to the narrow section of the male component's 18a hour-glass shaped area. As illustrated at FIG. 2, the exposed surface 22 on the interconnect base board 20a has a notch 36 that extends adjacent and parallel to the base board's 20 proximal end 26 length.
The step 40 has, as illustrated at FIGS. 2, 3, and 4, a stepped on surface 42, an opposite surface 44, an exposed end 46 and an unexposed end 48. At the unexposed end 48 on the interlocking step 40a is a protrusion 50. The notch 36 receives the protrusion 50.
Reverting to FIGS. 3 and/or 4, the step 40 on the opposite surface 44 has a groove section 52 and a female component 54 that respectively receive the riser's tongue section 16b and male component 18b. In particular the female component 54 has a rib area 56 that conforms to the narrow section of the male component's 18b hour-glass shaped area.
The base board 20 is installed onto the side wall 10 first by applying a force over the base board's female component 32 so the female component 32 receives the male component 18a. The protrusion 50 is then inserted into the notch 36 to ensure the proper alignment between (a) the base board and the step and (b) the step and the riser. Once the step is properly aligned, a force is applied to the step's female component 54 to receive the male component 18b. 
A problem with the current Leisure Accents step ladder is the step can be displaced when excess weight is applied to the steps. In particular when excess and abnormal pressure is applied to the step's exposed end 46, the step could be dislodged. This is a problem to be avoided.